The present invention relates to a disk surface inspection method and its apparatus for optically inspecting defects on a sample surface.
As a magnetic disk substrate, an aluminum (Al) substrate or a glass substrate is used. As the glass substrate, crystallized glass (SX) or amorphous glass (MEL) is used in accordance with purpose, and as the respective types of glass, plural types of glass having different ingredients are used.
In the glass substrate, a concentric circular continuous flaw or a discontinuous flaw occurs in some cases in the middle of process steps. Unless the step that caused the concentric circular flaw on the glass substrate is specified and a countermeasure is conducted quickly, a large number of glass substrates having the concentric circular flaw flow the production line. There is a probability of mass production of defective products.
On the other hand, the defects on the surface of the glass substrate are optically inspected using an optical inspection device. In the device for inspecting the surface of the glass substrate, there is a need for classification of detected defects for the purpose of distribution to high level process management and process step improvement. A detection optical system of a device for inspecting the surface of a magnetic disk substrate is generally provided with plural detectors. In addition to classification of minute defects using detection signals from these plural detectors, classification of defects is performed based on the feature of defect distribution shape in the magnetic disk surface.
As a conventional device for inspecting defects on the surface of a magnetic disk, Japanese Patent Application Laid-Open Publication No. 2000-180376 discloses irradiating a magnetic disk as an inspection subject sample with laser, receiving reflection light and scattered light from the magnetic disk surface with plural detectors, and classifying minute defects under photoreception conditions of the respective photoreceptors. Further, flat surface continuity of detected minute defects is determined, and classification is performed by defect length, linear defect and solid defect.
Further, Japanese Patent Application Laid-Open Publication No. 2001-66263 discloses a disk surface inspection device which detects a circle scratch formed on a disk surface as a defect using a light condensing unit with small solid angle provided in an elevation angle position corresponding to the directivity of predetermined scattered light on the same optical axis as that of laser emitted on the disk surface.
Further, Japanese Patent Application Laid-Open Publication No. 2006-352173 discloses defect classification in accordance with defect distribution status, including detecting linearly arrayed defects by Hough transform using defect position information obtained by inspection of the surface of a semiconductor wafer.
Further, Japanese Patent Application Laid-Open Publication No. 2011-122998 discloses generating a histogram of number of defects by substrate radius, and detecting circular scratch and island defect separately from other defects.